Underground mining (e.g., coal mining) typically necessitates the cutting of intersecting passageways throughout the mine. These intersecting passageways are often arranged in a grid pattern, with the passageways intersecting at right angles. (In other instances the passageways intersect at angles other than 90 degrees.) In addition to providing access, the passageways are also used for ventilation purposes. Some passageways are used to deliver fresh air into the mine while others to expel contaminated air from the mine. Where a fresh air passageway intersects a contaminated air passageway it is necessary to prevent mixing of the two air streams.
An overcast (also referred to as an undercast) is a structural system that is typically utilized in a mine or tunnel ventilation system. The overcast is constructed in a mine intersection for the purpose of preventing the mixing of the air in two intersecting passageways. For example, overcasts are used to prevent the mixing of ventilation (intake) air flowing through a first passageway and contaminated (exhaust) air flowing through a second passageway that intersects the first. Overcasts, however, can be time-consuming to assemble in place. In addition, not only are mine passageways a variety of shapes and sizes, not only intersections are at right angles. Because overcasts are intended to prevent the mixing of air in intersecting passageways, it is important that the overcast fit properly in the intersection so that sufficient sealing may be provided between the overcast and the mine ribs. Therefore, each overcast is typically sized and configured for the particular intersection in which it will be installed.
While a variety of devices and techniques may exist for providing overcast structures in mines, it is believed that no one prior to the inventors have made or used an invention as described herein.
The drawings are not intended to be limiting in any way, and it is contemplated that various embodiments of the invention may be carried out in a variety of other ways, including those not necessarily depicted in the drawings. The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention; it being understood, however, that this invention is not limited to the precise arrangements shown.